1. Field of the Invention
The present invention relates to a disk drive, and more particularly, a disk drive and method for efficiently storing zone control parameter sets in memory for reading and writing data on a plurality of disk surfaces.
2. Description of the Prior Art
Disk drives store large volumes of data on a plurality of disks mounted on a spindle assembly. Each disk includes two disk surfaces which are capable of storing data. On each disk surface, user data is divided into groups of sectors and stored in concentric circular tracks located between an outside diameter and inside diameter of the disk. Embedded servo information is recorded in servo sectors placed in radially continuous narrow wedges between the groups of sectors. The information contained in the servo sectors may include track number (address), sector number, timing, and tracking information for positioning a transducer head over the disk surface.
It is desirable to keep a maximum uniform density of data stored on the surface of each disk, while minimizing disk error rates. Data tracks located near the inside diameter of the disk surface are much shorter than data tracks located near the outside diameter of the disk surface. To compensate for these physical differences, zone recording techniques are utilized where the rate (i.e., frequency) at which data is written to the disk surface increases from the inside tracks to the outside tracks to assure a uniform density of data while maximizing disk storage capacity. Although the recording rate could theoretically be optimized for each track, parameter storage and performance limitations dictate a compromise by establishing discrete recording frequencies.
In zone recording, groups of adjacent tracks are assigned to an array of zones between the inside track and the outside track of the disk surface. For example, there may be ten to sixteen zones across the disk surface. Although data is written at the same recording frequency within each zone, the recording frequency increases from zone to zone as the transducer head moves from the inside zones to the outside zones. Zone recording techniques are employed to maintain disk performance, including minimizing disk recording error rates, while more fully utilizing the storage capacity of each disk surface.
Each disk surface has a transducer head associated with it for reading and writing data on the disk surface. Transducer heads are manufactured to meet desired performance requirements such that data may be written to and read from each disk surface while maintaining acceptable error rates. In high volume manufacturing of disk drives with multiple transducer heads, there will be instances when one or more of the transducer heads may not meet design specifications. The remaining transducer heads are of a quality capable of operating at or above desired performance levels. If the frequency of the data written on the surface of the disc exceeds the ability of the low performance transducer heads to reliably recover the data, those heads may be termed "stressed" resulting in a higher disk reading error rate.
A low performing transducer head greatly affects the performance rating of the disk drive. If nothing is done to compensate for the low performing transducer head, the disk drive may be rejected for failure to meet specifications. One way to improve the error rate is to modify control parameters, including lowering recording frequency parameters for the disk drive to be within the performance range of the low performing transducer heads. If the recording frequency parameters for corresponding zones on all the disk surfaces are lowered to improve the error rate for the low performing transducer head, the remaining transducer heads are subjected to operating at a level below that which they are capable of performing. The result of uniformly lowering frequency parameters is a disk drive operating at a level below its potential capacity.
To avoid capacity loss in the face of a low performing head, a disk drive can use modified control parameters for an array of zones of a given disk surface relative to corresponding zones on other disk surfaces. Recording frequency is reduced, and error rates are improved. Now, only one disk surface of the disk drive has reduced capacity. The control parameters for the remaining disk surfaces may be adjusted to result in slightly raised capacity to compensate for the lost capacity of the modified parameter surface.
Control parameters for each zone are stored in non-volatile memory. These control parameters are transferred to random access memory (RAM) upon disk drive start-up. By moving these control parameters into RAM, the disk drive has rapid access of these control parameters during disk drive operation, as the disk drive moves from disk surface to disk surface, and across each disk surface.
Use of modified control parameters requires an additional set of control parameters for each zone of the low performance disk surface to be stored into memory. FIG. 1 illustrates a prior art exemplary embodiment of a zone control parameter table stored in RAM for a disk drive having a set of control parameters for disk surfaces associated with a standard transducer head (TABLE 1) and a low performing transducer head (TABLE 2). Each disk surface has ten zones, wherein each zone is associated with a control parameter set stored in memory. Each control parameter set includes physical parameters which define the zone (such as number of sectors per track, skew values, etc.) and data channel related parameters (such as recording frequencies, thresholds, channel filter values, etc.), and as such, each control parameter set occupies a block of memory. Each respective zone of a disk surface associated with a standard transducer head uses a corresponding control parameter set in TABLE 1. For example, zone 1 uses control parameter set A, zone 2 uses control parameter set B, etc. In reference to the low performance transducer head, zones 1-10 of the associated disk surface are mapped to corresponding control parameter sets K-T of TABLE 2. By operating the low performance transducer heads using modified zone control parameters, the additional set of zone control parameters doubles the memory requirements in the table for storing zone control parameters. The resulting disk drive requires additional RAM for storing the modified control parameters and accordingly has less space available in RAM for other disk drive functions.